The invention is generally directed to toner and developer compositions, and more specifically, the present invention is directed to toner and developer compositions containing charge enhancing additives, which impart or assist in imparting a negative charge to the toner particles and enable toners with rapid triboelectric charging characteristics. In one embodiment, there are provided in accordance with the present invention toner compositions comprised of a polymer, or polymer resins, pigment, including color pigment particles or dye molecules, and certain metal complex composites which serve as a charge enhancing additive. In one embodiment, the present invention is directed to toner compositions with metal complex charge enhancing additives, which additives can be obtained from the reaction of a mixture of hydroxyaromatic compound like hydroxybenzoic acid, and a base with a mixture of a metal ion and an excess of an aromatic dicarboxylic acid. The metal complex charge enhancing additives in embodiments are believed to be comprised of or contain a metal complex component comprised of an anion with a central metal ion bonded to two different ligands, one hydroxybenzoic acid and one an aromatic dicarboxylic acid, and a counter cation of a proton, an alkaline metal ion or an ammonium ion. When an ortho-hydroxybenzoic acid and an aromatic ortho-dicarboxylic acid such as phthalic acid are employed as the two ligand precursors, the resulting effective metal complex component contains an anion structure in which the two ligands are chelated to the central metal in a bidentate manner. The charge additives in embodiments of the present invention enable, for example, toners with rapid triboelectric charging characteristics, extended developer life, stable triboelectric properties substantially irrespective of changes in environmental conditions, and high image print quality with substantially no background deposits. Also, the aforementioned toner compositions usually contain a colorant component comprised of, for example, carbon black, magnetites, or mixtures thereof, color pigments or dyes with cyan, magenta, yellow, blue, green, red, or brown color, or mixtures thereof thereby providing for the development and generation of black and/or colored images. The toner and developer compositions of the present invention can be selected for electrophotographic, especially xerographic imaging and printing processes, including highlight and full color processes.
Toners with negative charge additives are known, reference for example U.S. Pat. Nos. 4,411,974 and 4,206,064, the disclosures of which are totally incorporated herein by reference. The '974 patent discloses negatively charged toner compositions comprised of resins, pigment particles, and as a charge enhancing additive ortho-halophenyl carboxylic acids. Similarly, there are disclosed in the '064 patent toner compositions with chromium, cobalt, and nickel complexes of salicylic acid as negative charge enhancing additives. In U.S. Pat. No. 4,845,003 there are illustrated negatively charged toners with certain aluminum salt charge additives. More specifically, this patent discloses as charge additives aluminum complexes comprised of two or three hydroxybenzoic acid ligands bonded to one central aluminum ion. While these charge additives have the capability of imparting negative charge to toner particles, they are generally not as efficient in promoting the rate of triboelectric charging of toner particles. A fast rate of triboelectric charging is particularly important for high speed xerographic machines because they consume toners rapidly, and fresh toners have to be constantly added to keep the machines running. The added uncharged toners are, therefore, required to charge up to their equilibrium triboelectric charge level rapidly to ensure no interruption in the xerographic machine's operation. Another shortcoming of these charge additives is their thermal instability, and they often decompose during the thermal extrusion process of the toner manufacturing cycle. Additionally, the hydroxybenzoic acid ligands, particularly 3,5-di-tert-butylsalicylic acid, are costly; for research quantities, that is 1 kilogram or less, the cost of 3,5-di-tert-butylsalicylic acid is $250 per kilogram as compared to about $30 per kilogram for phthalic acid. About 50 percent less of 3,5-di-tert-butylsalicylic acid precursor can be selected for the preparation of the charge additive of the present invention, and the other 50 percent, or 1/2 replaced with phthalic acid precursor in embodiments. Many of the above disadvantages are eliminated, or substantially eliminated with the metal complex charge additives of the present invention.
Developer compositions with charge enhancing additives, which impart a positive charge to the toner particles, are also well known. Thus, for example, there is described in U.S. Pat. No. 3,893,935 the use of quaternary ammonium salts as charge control agents for electrostatic toner compositions; 4,221,856 which discloses electrophotographic toners containing resin compatible quaternary ammonium compounds in which at least two R radicals are hydrocarbons having from 8 to about 22 carbon atoms, and each other R is a hydrogen or hydrocarbon radical with from 1 to about 8 carbon atoms, and A is an anion, for example, sulfate, sulfonate, nitrate, borate, chlorate, and the halogens such as iodide, chloride and bromide, reference the Abstract of the Disclosure and column 3; a similar teaching is presented in U.S. Pat. No. 4,312,933 which is a division of U.S. Pat. No. 4,291,111; similar teachings are presented in U.S. Pat. No. 4,291,112 wherein A is an anion including, for example, sulfate, sulfonate, nitrate, borate, chlorate, and the halogens; U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference, discloses developer compositions containing as charge enhancing additives organic sulfate and sulfonates, which additives can impart a positive charge to the toner composition; and U.S. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference, discloses positively charged toner compositions with resins and pigment particles, and as charge enhancing additives alkyl pyridinium compounds.
Disclosed in copending patent application, U.S. Ser. No. 894,688, the disclosure of which is totally incorporated herein by reference, is a negatively charged toner composition comprised of a polymer or polymer resins, a colorant or colorants, optional surface additives, and a metal complex charge enhancing additive obtained from the reaction of a hydroxybenzoic acid and a base with a mixture of a metal ion and a hydroxyphenol.
Although many charge enhancing additives are known, there continues to be a need for charge enhancing additives which when incorporated into, or on toner compositions, provide toners with many of the advantages illustrated herein. There is also a need for negative charge enhancing additives which are useful for incorporation into black and colored toner compositions and which can be utilized for developing positive electrostatic latent images. Moreover, there is a need for colored toner compositions containing charge enhancing additives which do not substantially interfere with the color quality of the colorants present in the toners. Another need relates to the provision of toner compositions with certain charge enhancing additives, which toners in embodiments thereof possess substantially stable triboelectric charge levels, and display acceptable rates of triboelectric charging characteristics. Furthermore, there is also a need for toner compositions with certain charge enhancing additives which possess excellent dispersibility characteristics in toner resins, and can therefore form stable dispersions in the toner compositions. There is also a need for negatively charged black and colored toner compositions that are useful for incorporation into various imaging processes, inclusive of color xerography, as illustrated in U.S. Pat. No. 4,078,929, the disclosure of which is totally incorporated herein by reference; laser printers; and additionally a need for toner compositions useful in imaging apparatuses having incorporated therein layered photoresponsive imaging members, such as the members illustrated in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference. Also, there is a need for negatively charged toner compositions which have desirable triboelectric charge levels of, for example, from between about -10 to about -40 microcoulombs per gram, and preferably from about -15 to about -25 microcoulombs per gram, and triboelectric charging rates of less than about 120 seconds, and preferably less than 60 seconds as measured by standard charge spectrograph methods when the toners are frictionally charged against suitable carrier particles via conventional roll-milling techniques. There is also a need for nontoxic, substantially nontoxic, or environmentally compatible charge enhancing additives that can be incorporated at effective concentrations of, for example, less than 7 weight percent, and preferably less than 4 weight percent in toner compositions. The concentrations of the charge additives that can be utilized in embodiments generally ranges from about 0.05 weight percent to about 10 weight percent depending on whether the charge additive is utilized as a surface additive or as a dispersion in the bulk of the toner. An additional need resides in the provision of simple and cost-effective preparative processes for the metal complex composite charge enhancing additives of the present invention. Concentrations of toner in the developer (toner and carrier) particles are, for example, from about 0.5 to about 5 weight percent, and preferably from about 1 to about 3 weight percent.